[ foh-tuh-peer-ee-uh-diz-uhm ]

  1. the response, as affecting growth or reproduction, of an organism to the length of exposure to light in a 24-hour period.

Origin of photoperiodism

First recorded in 1915–20; photoperiod + -ism
  • Also called pho·to·pe·ri·o·dic·i·ty [foh-toh-peer-ee-uh-dis-i-tee]. /ˌfoʊ toʊˌpɪər i əˈdɪs ɪ ti/.

Words Nearby photoperiodism Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

British Dictionary definitions for photoperiodism


/ (ˌfəʊtəʊˈpɪərɪəˌdɪzəm) /

  1. the response of plants and animals by behaviour, growth, etc, to photoperiods

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for photoperiodism


[ fō′tō-pîrē-ə-dĭz′əm ]

  1. The response of an organism to changes in its photoperiod, especially as indicated by vital processes. For example, many plants exhibit photoperiodism by flowering only after being exposed to a set amount of daylight, as by requiring either a long or short day to flower. Plant growth, seed germination, and fruiting are also affected by day length. Photoperiodic responses in plants are regulated by special pigments known as phytochromes. In animals, migration, mating, amount of sleep, and other behaviors are also photoperiodic. In many animals, photoperiodism is regulated by the hormone melatonin.

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